Harmful effects of fetal and current exposure to tobacco smoke products

Our population-based epidemiologic study showed the harmful effects of fetal and current exposure to tobacco smoke products. Prenatal exposure due to maternal smoking had the strongest effects on respiratory symptoms. Current household ETS exposure also showed significant adverse effects, but past-only ETS exposure was not associated with any respiratory outcome. In addition, the number of current household cigarettes smoked, the percentage of ETS exposure during lifetime, and the number of current smokers at home showed increasing trends in risks of respiratory symptoms. Age, sex, active smoking habits, parental atopic history, and parental education might contribute to asthma and wheeze in childhood. We minimized interference from these confounders by recruiting lifelong nonsmokers of similar age at study entry, and adjusting potential confounders by regression models.
Although maternal smoking was, as expected, a strong determinant of preterm delivery and low birth weight, and these adverse pregnancy outcomes were strong predictors of respiratory problems, only gestational age showed an effect in our study. Adjustment for indoor residential factors resulted in only small changes in the effect estimates, and these covariates were not included in the final models. In our population, 197 (3.9%) children were reported to have had in utero ETS exposure. The prevalence is much lower than other Western studies.

We found that in utero exposure to maternal smoking had larger effects on early-onset asthma than those asthmatics diagnosed after 5 years of age. Previous studies showed a stronger risk for incident asthma or wheezing illness among younger children compared with older children. These investigators suggested that the stronger relationship might be attributed to exacerbation of intercurrent infection among young children, resulting in transient wheeze that would tend to diminish with age and increasing airway caliber. The proposed mechanism would suggest that household ETS may not be the sole primary cause of early childhood asthma.

In summary, our results showed that prenatal and current household ETS exposure in Taiwan had significant adverse effects on respiratory health in children. Eliminating household ETS exposure may offer the most promising opportunity for reducing morbidity, because this risk factor is potentially modifiable. Public health policy for reducing the burden of respiratory symptoms may require a stronger focus on smoking cessation in the home, where children could gain significant health benefits.